Arrangement for dynamic balancing of a high speed press

ABSTRACT

A high speed mechanical press having two parallel counterrotating crankshafts with a reciprocating slide connected thereto and with off center masses fixed to the crankshafts in distributed relation therealong for counterbalancing the inertia forces developed on the crankshafts by the reciprocating components of the press and the centrifugal forces developed on the crankshaft by off center masses acting thereon at the throw portions of the crankshafts.

United States Patent 11 1 Voorhees et al.

[111 3,797,327 1451 Mar. 19, 1974 ARRANGEMENT FOR DYNAMIC BALANCING OF AHIGH SPEED PRESS [75] Inventors: John E. Voorhees, Sidney; Donald J.Hemmelgarn, Minster, both of Ohio [73] Assignee: The Minster MachineCompany, Minster, Ohio 22 Filed: Sept. 5, 1972 21 Appl. No.: 286,122

[52] US. Cl 74/604, 72/429, 100/292 [51] Int. Cl Fl6f 15/10 [58] Fieldof Search 74/604, 603; 123/192 B,

[56] l References Cited UNITED STATES PATENTS 10/1957 Jackson 74/6045/1938 Burkhardt I 3/1926 Walker 74/603 3,402,707 9/1968 Heron 74/604 X3,415,237 12/1968 Harkness r 1 74/604 X 3,555,586 l/l97l Wisebaker72/429 X Primary Examiner-Benjamin W. Wyche Assistant Examiner-4 D.Shoemaker Attorney, Agent, or Firm-Albert L. Jeffers; Roger M. Rickert 7ABSTRACT A high speed mechanical press having two parallelcounterrotating crankshafts with a reciprocating slide connected theretoand with off center masses fixed to the crankshafts in distributedrelation therealong for counterbalancing the inertia forces developed onthe crankshafts by the reciprocating components of the press and thecentrifugal forces developed on the crankshaft by off center massesacting thereon at the throw portions of the crankshafts.

7 Claims, 4 Drawing Figures PATENTED UAR 19 1974 SHEET 2 OF 2ARRANGEMENT FOR DYNAMIC BALANCING OF A HIGH SPEED PRESS This inventionrelates to an arrangement for dynamic balancing a high speed press, andis particularly concerned with the dynamic balancing of a highspeedmechanicai press having a pair of counterrotating crank shafts in thepress crown connected to a reciprocating slide. 7

Mechanical presses, including presses with counterrotating crankshaftsare known, but do not usually operate at such high speeds that seriousforces of unbalance occur anywhere in the press structure. It iscontemplated, however, to operate such presses up to speeds of 1600strokes a minute, or more, and at these operating speeds, forces ofunbalance can reach substantial proportions. For example, the slide ofthe press and the parts connected thereto reciprocate between a top deadcenter position and a bottom dead center position and developsubstantial forces of unbalance due to inertia forces created by themovement of the reciprocating components.

Further, the slide isdriven by a pair of rotating crankshafts, each ofwhich has a throw portion and forces of unbalance can be created byeccentric mass disposed at the throw portion of each crankshaft or soconnected to the throw portions of the crankshaft as to be consideredrotating therewith.

A primary object of the present invention is the provision of anarrangement for counterbalancing the aforementioned inertia andcentrifugal forces of unbalance that can be created in a pressarrangement of the nature referred to and, particularly, inconnectionwith high speed presses.

A further object is the provision of a system for calculating the sizeand disposition of counterbalancing masses. to produce the best dynamicconditions in respect of a high speed press of the nature referred to.

These and other objects and advantages of the present invention willbecome. more apparent upon reference to the following detailedspecification taken in connection with the accompanying drawings inwhich:

FIG. 1 is a somewhat schematic perspective view showing the basicarrangement of that part of a press structure that is counterbalancedaccording to the present invention.

FIGS. 2, 3 and 4 show the rotating and reciprocating components of thepress structure and the counterbalancing masses associated therewith inthree different positions of operation.

BRIEF SUMMARY OF THE INVENTION According to the present invention, apress is provided with a pair of crankshafts geared together to rotatein respectively opposite directions and each having a throw portionconnected by a connecting rod with the upper end of a piston member, thelower end of which is fixed to a press slide.

For counterbalancing the inertia forces created by the reciprocatingcomponents of the press and the centrifu gal forcescreated by unbalancedmass rotated with the crankshaft, counterbalancing mass elements arefixed to the crankshafts to rotate therewith. These elements areconstructed and arranged to develop'forces on the crankshaftsubstantially balancing the aforemen- DETAILED DESCRIPTION OF THEINVENTION Referring to the drawings somewhat more in detail,

in FIG. 1, a first crankshaft is indicated at A and a second crankshaftat B. Crankshafts A and B are parallel and are geared to rotate togetherby the gears Ga and Ch. Crankshaft A has a throw portion Ta thereon andcrankshaft B has a throw portion Tb thereon. The cranks'hafts areidentical in every respect, and the throw portions are so oriented onthe respective crankshafts that both reach top and bottom dead center atthe sanie instant.

Mounted on crankshaft A on one side of the throw portion thereof isacounterweight, the center of mass of which, indicated at Mwa, isdirectly opposite in the radial direction from the center of mass Mr ofthe throw portion Ta. The radius of eccentricity of center of mass Mwaisindicated by the radius Rwa in FIG. 1, while the radius ofeccentricity of the center of mass Mr of throw portion Ta is indicatedby the radius Rs.

The axial distance of center of mass Mwa from center of mass Mr isindicated by the dimension Lwa.

On the opposite side of throw portion Ta of shaft A, the gear Ga isindicated as having a center of mass Mga which has a radius ofeccentricity Rga which is parallel to the radius of eccentricity Rwapreviously referred to. The axial distance from the center of mass Mgaof gear Ga to the center of mass Mr of throw Ta of crankshaft Aisindicated by the dimension Lga.

The crankshafts are shown with the throws in the bottom of dead centerpositionand in this position the off center mass at the throw portion ofthe crankshaft is developing a force Fca directed vertically downwardlywhereas the force developed by offcenter mass Mga of gear Ga isindicated at Fga and acts vertically upwardly while the force directedby mass Mwa of the counterweight is indicated by F wa and actsvertically upwardly. r

The same off center masses and the dimensions pertaining thereto and theforces developed by the off center masses are indicated by the samereference characters on shaft B, except that the final letter of eachindif cation is b instead of a.

The slide of the press is indicated at S and connected thereto are twopistons Pa and Pb, the upper ends of which are pivotally connected tothe lower ends of connecting rods Ca and Ch respectively, the upper endsof which are engaged by the respective crankshaft throws.

The crankshafts are rotatably supported in the press crown and thepistons are reciprocably guided in the press crown with the press crownbeing schematically indicated by reference numeral 10 in FIG. 1.

The reciprocating components of the arrangement, and which includes theslide Sand the pistons Pa and Pb and substantial portions of theconnecting rods Ca and Cb, have a center of mass Ms which develops aninertia force indicated at Fs and which may be directed either upwardlyor downwardly depending on the position of the slide in its stroke.

The off center mass for the gears Ga can advantageously be arrived at bydrilling holes 12 in the gears, but it is also possible to attach offcenter mass to the gears if preferred.

FIGS. 2, 3 and 4 show the slide S of the press at bottom dead center,mid stroke and top dead center, respectively, and illustrate also thedirections of the inertia and centrifugal forces which are acting on therespective crankshafts.

For smooth, vibration free, operation of the press at high speeds, theforces of unbalance in the form of the primary inertia forces developedby the reciprocating components as well as the centrifugal forcesdeveloped by rotating unbalanced mass on the crankshafts aresubstantially balanced out by the arrangement described above.

In defining the balancing system, it is necessary to determine the totalamount of the reciprocating mass, which has been referred to as Ms andwhich includes the mass of the slide, the pistons and that portion ofthe masses of the connecting rods which reciprocate, together with thewrist pins that connect the connecting rods to the pistons and theweight of the die part that is attached to the slide. The die parts willvary somewhat in weight, but it has been found that for a given machine,the die parts will average about the same weight so that a fixedcounterbalance system has been found to be quite satisfactory.

If necessary, the weight of the die part on the slide could be adjustedto a predetermined amount, if so desired, thereby to provide forsubstantially balancing the system.

In effecting the calculations leading to the determination of thecounterbalancing necessary and the dispositions thereof with respect tothe radii of eccentricity thereof and the axial disposition of thecounterbalancing masses along the crankshaft, the following dimensionsand values are employed: 1

Ms Total mass of reciprocating components.

Rs Crank throw eccentricity.

Fs Peak value of the primary component of the total reciprocating slideinertia force.

Fc Centrifugal unbalance force developed by the rotating mass of thecrank throw portion and the portion of the mass of one connecting rodthat may be considered to rotate with its crankshaft.

S Stroke of press slide.

Mr The mass of one crank throw portion together with the portion of oneconnecting rod that may be considered to rotate with the crankshaft.

Mga Mass of gear on Shaft A.

Mgb Mass of gear on Shaft B.

Rga Eccentricity of center of gravity of gear mass on Shaft A.

Rgb Eccentricity of center of gravity of gear mass on Shaft B.

F ga Centrifugal force developed by rotating gear on Shaft A.

Fgb Centrifugal force developed by rotating gear on Shaft B.

Lga Length along Shaft A from connecting rod centerline to center ofgravity of gear.

Lgb Length along Shaft B from connecting rod centerline to center ofgravity of gear.

Mwa Mass of balancing weight carried on Shaft A.

Rwb Radius from shaft centerline to center of gravity of balancingweight carried on Shaft B.

Fwa Centrifugal force developed by rotating balancing weight carried onShaft A.

5 F wb Centrifugal force developed by rotating balancing weight carriedon Shaft B.

Lwa Length along Shaft A from connecting rod centerline to center ofgravity of balancing weight carried on Shaft A.

Lwb Length along Shaft B from connecting rod centerline to center ofgravity of balancing weight carried on Shaft B..

N Angular velocity of Shafts A and B which are seen to be gearedtogether to rotate in opposite directions at the same speeds. The peakvalue of the primary inertia forces developed by the reciprocating slideassembly is given by:

Fs= Ms Rs N This force varies sinusoidally with crankshaft rotationreaching its peak downward valueat the time that the slide is at thebottom of its stroke and reaching its peak upward value at the time theslide is at the top of its stroke.

In addition to the reciprocating unbalance force the rotating unbalanceforce developed on each of the two crankshafts given by the following:

The balance correction forces are given by the following relationships:

Fga Mga Rga N For the best balance correction the followingrelationships should applyr Fga Fwa 0.5 F: F0

Fga Lga Fwa L va Fgb Fwb 0.5 Fs Fe Fgb Lgb Fwb Lwb Mwb Mass of balancingweight carried on Shaft B. 6

Rwa Radius from shaft centerline to center of gravity of balancingweight carried on Shaft A.

Substituting equations (1) thru (6) in equations (7) thru 10) andeliminating N yields the following relationships for proper balancing:

Mga Rga Mwa Rwa 5 Rs (0.5 Ms Mr) Mga Rga Lga Mwa Rwa Lwa Mgb Rgb Mwb RwbRs (0.5 Ms Mr) Mgb Rgb Lgb Mwb Rwb Lwb It is clear from the aboverelationships that the designer retains a great deal of latitude ofchoice in the placement of the balancing weights on the presscrankshafts and in the magnitude of these weights. In the particulardesign illustrated the weights near one end of the crankshaft were madeintegral with the gears that couple the shafts together by boring holesthrough one side of these gears to displace the center of gravity of thegears away from the shaft centerline. An equivalent effect could havebeen produced by bolting or otherwise fastening weights to the gears, orby leaving the. gears uniform and by adding weights at another locationnear the'gear end of the shafts.

So long as the relationships expressed by equations (12) and (14) aremaintained no tipping moment will be developed by the balancing weightson either crankshaft. So long as the relationships expressed byequations (11) and (13) are maintained the net balancing force will becorrect on each crankshaft.

FIGS. 2, 3 and 4 show the manner in which the rotating balancing forcesinteract with the reciprocating press slide inertia forces at bottomdead center, midstroke, and top dead center. As can be seen from thesefigures, at the top and bottom dead center positions, the forcesdeveloped by the rotating balance weights are equal and opposite to theprimary slide inertia force together with the rotating unbalance. At themid-stroke position where, no primary slide inertia force is developedthe rotating weights produce equal and opposite horizontal forcecomponents which cancel one another out without producing anynetreaction tending to move the press structure.

The overall effect is that the only balancing errors in the system aredue to (a), secondary inertia forces which are quite small with thetypical large ratio of connecting rod length to crank throw eccentricityin a press, and (b), the error due to the die weight on the press slidenot being identically equal to the value for which the balancing systemwas designed. This latter error may be made as small as desired bydesigning the press balancing system for the heaviest expected dieweight and then by adding the necessary weight to the slide in each caseso that the weight of the die in use, plus the added weight, is alwaysequal to the design value. In practice, the die weight error to beexpected in a'given size press will usually not be sufficient to justifythe added complication of this correction procedure. t

It should also be noted that a press utilizing a scotch yoke mechanismto actuate the slide in place of the connecting rod mechanism of thepresent design illustrated develops no secondary slide inertia force,and hence would provide a more perfect degree of balanc- A modificationof the balancing method described may distribute any one or all of thebalancing weights into two or more parts located in the same ordifferent planes along the shafts. The overall effect of subdividing theweights in this manner will be the same as if the equivalent totalweight were placed at the location of the center of gravity of thesubdivided weights.

From the foregoing, it will be apparent that there is not onlycontemplated the balancing of the crankshafts by gears at one end havingan off center weight and a counterweight near the other end having anoff center weight, but it is also contemplated that a plurality ofcounterweights could be distributed along each crankshaft in positionstherealong determined in the manner indicated above.

Modifications may be made within the scope of the appended claims.

What is claimed is:

1. In a press having a crown and a slide reciprocable relative to thecrown; a pair of parallel crankshafts rotatable in the crown, means fordrivingsaid crankshafts in counter'rotation, each crankshaft havingthrow portions and connecting means connecting said throw portions tothe slide for driving the slide in reciprocation as the crankshaftsrotate, and means for substantially counterbalancin'g the inertiaforces. developed by the reciprocating slide and connecting means andthe centrifugal forces developed on the crankshafts by eccentric massdisposed at said throw portions, said means comprising mass elementmeans eccentrically mounted on said crankshafts, said mass element meansbeing not all of equal magnitude or distance from the centerline of thereciprocating slide and oriented on the respective crankshafts so as tobe in opposed relation when the slide is about midway in the strokethereof and in cumulative relation when the slide is at the ends of thestroke thereof.

2. A press according to claim 1 in which said connecting means includesa pair of pistons each fixed at one end to the slide and extendinginparallel relation from the slide toward the crankshafts and each pistonin the plane of the axis of arespective crankshaft, said connectingmeansalso including connecting rods each having one end engaging thethrow portion of a respective crankshaft and, the other end pivotedtothe other end of a respectivepiston, said pistons being adapted forbeing guided for axial reciprocation in the press crown.

3. A press according to claim 1 in which the amount of mass of saidmasselement means and the radius of eccentricity thereof relative to therespective crankshaft is substantially determined by the formula:

Mm Rm Rs (0.5 Ms Mr) where Mm mass of mass element means pertaining tothe crankshaft Rm radius of eccentricity of the mass of the mass elementmeans Rs radius of eccentricity of the throw portion of the crankshaftMs mass of reciprocating components Mr= mass of throw portion of thecrank shaft and the portion of the pertaining connecting rod that can beconsidered to rotate therewith. 4. A press according to the claim 31 inwhich said mass element means for each crankshaft comprises at least twomass elements in axially spaced relation on the respective crankshaft.

A press according to claim 3 in which each crankshaft has first andsecond mass elements mounted thereon and the amount of mass in therespective element and the radius of eccentricity thereof relative tothe respective crankshaft is substantially determined by the formula:

Mga Rga Mwa Rwa Rs (0.5 Ms Mr) where Mga mass of first mass element Rgaradius of eccentricity of first mass element Mwa mass of second masselement Rwa radius of eccentricity of second mass element Rs radius ofeccentricity of the throw portion of the crankshaft Ms mass ofreciprocating components Mr mass of throw portion of the crankshaft andthe portion of the pertaining connecting rod that can be considered torotate therewith.

6. A press according to claim 5 in which said first and second masselements are mounted on opposite axial sides of the throw portion of therespective crankshaft with the axial spacing Lga of the said first masselement from said throw portion related to the axial spacing Lwa of thesaid second mass element from the said throw portion according to theformula: Mga Rga Lga Mwa Rwa Lwa.

7. A press according to claim 1 in which the mass element meanspertaining to each crankshaft comprises a plurality of mass elementsmounted thereon in axially distributed relation and on opposite axialsides of the throw portion thereof, the amount of mass in the respectivemass elements and the radius of eccentricity thereof relative to theaxis of the respective crankshaft and the axial location of each masselement relative to the throw portion of the crankshaft is substantiallydetermined by the following formulae:

EMr Rr Lr 2M1 R1 L1 ZMr Rr 2M1 R1 Rs (0.5 Ms Mr) where:

Mr= mass of each mass element on one side of throw portion of thecrankshaft Rr= radius of eccentricity of the respective mass element Lraxial distance of the respective mass element from the throw portion ofthe crankshaft M1 mass of each mass element on other side of throwportion of the crankshaft R1 radius of eccentricity of the respectivemass element 1 L1 axial distance of the respective mass element from thethrow portion of the crankshaft Rs radius of eccentricity of the throwportion of the crankshaft Ms mass of reciprocating components Mr= massof throw portion and that part of the connecting rod that can beconsidered to rotate therewith.

1. In a press having a crown and a slide reciprocable relative to thecrown; a pair of parallel crankshafts rotatable in the crown, means fordriving said crankshafts in counterrotation, each crankshaft havingthrow portions and connecting means connecting said throw portions tothe slide for driving the slide in reciprocation as the crankshaftsrotate, and means for substantially counterbalancing the inertia forcesdeveloped by the reciprocating slide and connecting means and thecentrifugal forces developed on the crankshafts by eccentric massdisposed at said throw portions, said means comprising mass elementmeans eccentrically mounted on said crankshafts, said mass element meansbeing not all of equal magnitude or distance from the centerline of thereciprocating slide and oriented on the respective crankshafts so as tobe in opposed relation when the slide is about midway in the strokethereof and in cumulative relation when the slide is at the ends of thestroke thereof.
 2. A press according to claim 1 in which said connectingmeans includes a pair of pistons each fixed at one end to the slide andextending in parallel relation from the slide toward the crankshafts andeach piston in the plane of the axis of a respective crankshaft, saidconnecting means also including connecting rods each having one endengaging the throw portion of a respective crankshaft and the other endpivoted to the other end of a respective piston, said pistons beingadapted for being guided for axial reciprocation in the press crown. 3.A press according to claim 1 in which the amount of mass of said masselement means and the radius of eccentricity thereof relative to therespective crankshaft is substantially determined by the formula: Mm RmRs (0.5 Ms + Mr) where Mm mass of mass element means pertaining to thecrankshaft Rm radius of eccentricity of the mass of the mass elementmeans Rs radius of eccentricity of the throw portion of the crankshaftMs mass of reciprocating components Mr mass of throw portion of thecrank shaft and the portion of the pertaining connecting rod that can beconsidered to rotate therewith.
 4. A press according to the claim 3 inwhich said mass element means for each crankshaft comprises at least twomass elements in axially spaced relation on the respective crankshaft.5. A press according to claim 3 in which each crankshaft has first andsecond mass elements mounted thereon and the amount of mass in therespective element and the radius of eccentricity thereof relative tothe respective crankshaft is substantially determined by the formula:Mga Rga + Mwa Rwa Rs (0.5 Ms + Mr) where Mga mass of first mass elementRga radius of eccentricity of first mass element Mwa mass of second masselement Rwa radius of eccentricity of second mass element Rs radius ofeccentricity of the throw portion of the crankshaft Ms mass ofreciprocating components Mr mass of throw portion of the crankshaft andthe portion of the pertaining connecting rod that can be considered torotate therewith.
 6. A press according to claim 5 in which said firstand second mass elements are mounted on opposite axial sides of thethrow portion of the respective crankshaft with the axial spacing Lga ofthe said first mass element from said throw portion related to the axialspacing Lwa of the said second mass element from the said throw portionaccording to the formula: Mga Rga Lga Mwa Rwa Lwa.
 7. A press accordingto claim 1 in which the mass element means pertaining to each crankshaftcomprises a plurality of mass elements mounted thereon in axiallydistributed relation and on opposite axial sides of the throw portionthereof, the amount of mass in the respective mass elements and theradius of eccentricity thereof relative to the axis of the respectivecrankshaft and the axial location of each mass element relative to thethrow portion of the crankshaft is substantially determined by thefollowing formulae: Sigma Mr Rr Lr Sigma M1 R1 L1 Sigma Mr Rr + Sigma M1R1 Rs (0.5 Ms + Mr) where: Mr mass of each mass element on one side ofthrow portion of the crankshaft Rr radius of eccentricity of therespective mass element Lr axial distance of the respective mass elementfrom the throw portion of the crankshaft M1 mass of each mass element onother side of throw portion of the crankshaft R1 radius of eccentricityof the respective mass element L1 axial distance of the respective masselement from the throw portion of the crankshaft Rs radius ofeccentricity of the throw portion of the crankshaft Ms mass ofreciprocating components Mr mass of throw portion and that part of theconnecting rod that can be considered to rotate therewith.